1. Field of the Invention
The present invention relates generally to a buck-boost converter, and more particularly to a synchronous rectifying buck-boost converter, which utilizes a transistor with low resistivity rather than a diode for converting DC low voltage input power to DC high voltage output power and vice versa.
2. The Prior Arts
It requires different amount of DC current, such as 5V, 3V or much lower 1.8V, for operating a common electronic device or electrical product, An (Light Emitting Diode) LED device, consisting of LEDs connected in series or parallel, requires several two digit numbers of power source for illuminating the LEDs. In addition, a motor generally requires 12V power source for operating the same or even more DC for operating the same.
In the prior art technique, a synchronous rectifying technique is applied to a buck or boost circuit so as to convert an actual DC power source into a required amount of voltage power. In practical application, two diodes together with a capacitor and one or two inductors are implemented in order to control the conductivity of two diodes so as to charge/discharge the capacitor, thereby generating an output power source.
It is noted that the diodes of the conventional technique encounter a relatively high resistivity and if the same is applied to a conversion circuit in a high electrical field may result in high power loss. Under the trend of carbon reduction scheme, EC has recently declared restrictions the date beginning from which aged and large carbon-production electronic or electrical appliances are to be dumped out or discarded. Hence, it is highly desirable to develop a synchronous rectifying buck-boost converter for used in electronic or electrical appliances so that production of carbon is reduced, thereby satisfying the trend of carbon reduction.